The present invention relates to a method and embedded bus bar structure for implementing power distribution in an electronic system.
Current and future high performance computer systems and server systems rely on both large-scale packaging of multiple high density interconnect modules and printed circuit boards. High signal speed integrated circuit devices are being fabricated in increasingly smaller sizes and requiring increasing numbers of connector pins or other connection interface structures within a spatial footprint.
LGA (Land Grid Array) module attach technologies have been used for the attachment of large ceramic modules to the backplane within computer systems for the last several years. LGA connection systems essentially clamp a formable connector pad between a substrate and the board by applying pressure from a backing plate, typically using a planar stiffener, and the module lid, cap, or heatsink. Bussing power on the topside of the card or board can force changes in the area of the LGA module which would cause significant requalification testing for the module connection technology. These types of connection technologies rely on flatness, stiffness, and generally a uniform structure underneath the LGA connection system to perform consistently.
Traditional planar stiffeners are needed to contact the printed circuit board or backplane and provide support for connectors and other large components such as heatsinks and land grid array (LGA) modules. These contact areas restrict where logic components can be placed. Often one whole side of the printed circuit board is consumed by stiffeners which restricts major components to a single side of the card or board. With all of the major and normally largest power consuming components on one side of the card, the use of traditional bus bars adds more competition for space and airflow.
U.S. Pat. No. 5,748,451, issued May 5, 1998 to Thompson et al. and assigned to the present assignee, discloses a backplane assembly that includes stiffeners to provide both mechanical stiffening and electrical power distribution. A power distribution system comprises a backplane, a power stiffener having alternate layers of dielectrics and conductors proximately located to the backplane, and removable connection to electrically connect the conductors in the stiffener to the backplane. Because power can be transferred directly to the backplane from the stiffener via the connection, the need for power cables and bus bars on the backplane is eliminated. In addition, noise suppressing capacitors may be located on the power stiffener, close to the load source.
Around Ground Design is a design approach currently being increasingly utilized in the layout of a printed circuit board (PCB). The approach essentially references signals to only ground as they are routed around the system. This is done to simplify retum-current or image currents issues. By employing this approach, there is often an unbalanced amount of ground plane requirements (for routing of signals) than would otherwise be used in traditional ground-signal-voltage-signal-ground stackup methodologies. This unbalanced approach can make it impossible to get enough power plane copper within the card or board stackup to support the voltage distribution requirements while providing sufficient ground plane surfaces to reference the signals. This leads to the need for additional power distribution elements such as bus bars. Those additional elements compete for volume, block airflow, and generally complicate the layout of the logic board if allowed to be on the component side of the card or board.
As system design gets more complex, the number of required core and input/output (I/O) voltage domains as well as legacy voltage levels continues to increase, causing multiple voltage domains to be contained on a single layer in the board design. As a result, significant routing issues arise as well as degradation of signal quality. Reducing the number of voltage domains will reduce the number of voltage domains splits, which is a gap between two voltage domains on a card. If critical signal wiring is routed over one of these splits, the signal is degraded due to multiple effects i.e. increased inductance in the retum-current path, large potential buildups at boundary between domains. A common practice is to not allow any critical wiring to cross these power planes splits which decreases board routability; however, tradeoffs also are made to allow signals to cross these voltage domains splits.
A need exists for an improved mechanism for implementing power distribution in an electronic system.
As used in the present specification and claims, the term printed circuit board or PCB means a substrate or multiple layers (multi-layer) of substrates used to electrically attach electrical components and should be understood to generally include circuit cards, printed circuit cards, backplanes, printed wiring cards, and printed wiring boards.
A principal object of the present invention is to provide a method and embedded bus bar structure for implementing power distribution in an electronic system. Other important objects of the present invention are to provide such method and embedded bus bar structure for implementing power distribution substantially without negative effect and that overcome some of the disadvantages of prior art arrangements.
In brief, a method and embedded bus bar structure are provided for implementing power distribution in an electronic system. A stiffener includes an embedded power bus bar structure for distributing power. The embedded power bus bar structure has a predefined pattern within a selected area of the stiffener. The selected area is separated from at least one predefined area. A printed circuit board is mounted to the stiffener and electrically connected to the embedded power bus bar structure.
In accordance with features of the invention, the embedded power bus bar structure can include multiple spaced apart power bus bars, enabling the power distribution of multiple voltage levels. The predefined pattern of the embedded power bus bar structure within the selected area of the stiffener is separated from each predefined site for a Land Grid Array (LGA). The embedded power bus bar structure in the stiffener does not affect the stiffener area under each LGA module connected to the printed circuit board.